A data transmission system of this type comprises at least two devices. According to its purpose, a first device is carried on the body by a patient and, in operation, generates medically relevant data that are transmitted to a second device in a wireless manner. The first device typically is a measuring device that uses a sensor in or on the body of a patient to make measurements and generates measuring data as medically relevant data that are transmitted to the second device. However, the first device can just as well be a treatment device, for example an infusion device that administers a medical agent, in particular insulin. The medically relevant data that are generated by a treatment device of this type typically are treatment data, for example infusion rates or similar data.
The second device of a medical data transmission system of this type typically serves for display, analysis of the medically relevant data generated by the first device and/or control of the first device.
In the first device, the medically relevant data are generated by a circuit, which contains, for example, a sensor for in-vivo measurement of an analyte concentration, and are transmitted to the second device by an internal communication unit in a wireless manner. The data generated by the circuit is initially stored in a handover memory from which they can be read-out by the communication unit. It is therefore necessary for both the data-generating circuit and the communication unit to have access to the handover memory. In order to avoid collisions, known data transmission systems with direct access (random access) to data have defined access rules and control mechanisms.
WO 2006/133851 A2 teaches the use of a handover memory in a medical data transmission system, which handover memory has a separate data input and data output each for the circuit and the communication unit. Although simultaneous access to the handover memory by the circuit and the communication unit is unlikely, it can lead to significant problems in particular if predefined protocols for communication with the second device, for example Bluetooth, are used.
Asynchronous communication processes involving access of different system components to a common memory must therefore be expected to be associated with a higher probability of data corruption. This necessitates a greater effort for safeguarding data, for example the use of buffer memories for short-term temporary data storage, and, in addition, a higher level of coordination and control between the participating system components.
It is known from U.S. Pat. No. 6,571,128 B2 to prevent access conflicts of the data-generating circuit and the communication unit of a medical data transmission system with regard to a common memory in that the data-generating circuit contains a microprocessor as master and the communication unit contains another microprocessor as slave. Although access conflicts can be precluded by this means, access of the communication unit to the handover memory is possible only in a restricted manner. Another disadvantage is that, in the case of a master processor defect, the microprocessor of the communication unit usually can no longer access the handover memory at all and, as a consequence, all data stored in the handover memory are lost. This is particularly serious if data are transmitted only relatively rarely, for example at intervals of approximately one week, from the first device to the second device.